Borehole apparatus



June 4, 1963 BLAGG BOREHOLE APPARATUS s sheets-sheet x Filed June 19.1959 Leon .B/ayg' IN VEN TOR.

ATRNEY June 4, 1963 L. BLAGG 3,092,182

BOREHOLE APPARATUS Filed June 19. 1959 5 Sheets-Sheet 2 een B/qyyINVENTOR.

ATR/VEY June 4, 1963 L. BLAGG 3,092,182

BOREHOLE APPARATUS Filed June 19. 1959 5 Sheets-Sheet 3 VERT/CAL 4X/Jecn /agg' 1N VEN TOR.

Arf/ML Exif/vr@ of /a'UwM June 4, 1963 L. BLAGG 3,092,182

BoREHoLE APPARATUS Filed June 19. 1959 5 Sheets-Sheet 4 een B/OgyJNVENTOR.

BY @JWM United States Patent O 3,092,182 BQREHLE APPARATUS Leon Riagg,Channelview, Tex., assigner to Schlumberger Weil Surveying Corporation,Houston, Tex., a corporation of Texas Filed .inne 19, 1959, Ser. No.821,636 19 Claims. (Ci. 16S-241) This invention relates to boreholeapparatus and, more particularly, pertains to new and improved apparatusespecially useful for maintaining an instrument in a selected positionrelative to the borehole axis or sidewall during a traverse of theborehole.

Various mechanisms lare available either for centering or foreccentering an instrument in a borehole or for maintaining awall-engaging instrument in contact with the sidewall of the borehole asthe instrument is passed through. One such mechanism, comprised of anarray of bowed springs, has been used heretofore with considerablesuccess. For example, several springs distributed equally about aninstrument can be used to center it in a borehole. However, bowed springarrangements are limited in their working range of borehole diameters.This is understandable because for a spring of given length, lateralbiasing force decreases as a function `of borehole diameter. Thus, thebowed springs may have to be of prohibitive length in order toaccommodate large changes in diameter. in addition, for a wide range ofborehole diameters, it is ordinarily necessary to utilize springs whoserestoring forces are relatively weak. Consequently, in a boreholesection of appreciable inclination, a spring on the low side of theinstrument is almost entirely collapsed by the weight of the instrument,and centering action is impaired. Further, a long bowed spring may bendin several different modes so that centering action may not always beconsistent.

It is, therefore, an object of the present invention to provide new andimproved apparatus for positioning an instrument in a borehole anduseful in a relatively wide range of borehole diameters.

Yet another object of the present invention is to provide new andimproved apparatus for positioning an instrument in a borehole and ofcomparatively small longitudinal dimensions.

A further object of the present invention is to provide new and improvedapparatus for positioning an instrument in a borehole and featuring aselected force versus lateral deiiection characteristic.

A still further object of the present invention is to provide new andimproved apparatus for positioning an instrument in a borehole andaording a relatively constant force versus lateral deiiectionchmacteristic over a given range of borehole diameters.

Another object of the present invention is to provide new and improvedapparatus for positioning an instrument in -a borehole in a consistentand highly eifective manner.

Borehole apparatus in accordance with the present invention is comprisedof a support assembly adapted to be passed through a borehole. Thesupport assembly includes a support member having a guide sectionextending longitudinally relative to the borehole and a pair ofmountings carried by the support member. One `of the mountings isoperatively associated with the guide section for movement relative tothe other mounting. The apparatus further comprises a .pair lof armswhich include -adjacent portions pivotally connected to one another andopposed portions pivotally connected to respective ones of themountings. The axes of at least two of the pivot-al connections arenon-parallel to one another and one of the arms includes a resilientportion. Thus, the arm containing the resilient portion is adapted toflex upon the Patented June 4, 1963 ICC application thereto of a bendingmoment so as to bias the adjacent portions of the arms away from thesupport assembly and toward the sidewall of the borehole.

The novel features of lthe present invention are set forth withparticularity in the appended claims. 4The present invention, both as toits organization and manner of operation together with further objectsand advantages thereof, may best be understood by reference to thefollowing description .taken in connection with the accompanyingdrawings in which:

FIG. l is a view in side elevation of apparatus constructed inaccordance with the present invention shown in operative conditionwithin a borehole drilled into the earth;

FIG. 2 is a cross-sectional view .taken along line 2 2 of FIG. l;

FIG. 3 is a view similar to the lone illustrated in FIG. l, but taken inthe direction of arrow 3;

FIGS. 4A and 4B are cross-sectional views taken along lines 4er- 4A and4B-4B, respectively, of FIG. l;

FIG. 5 is similar to FIG. 3, but illustrates the apparatus in diierentcondition of operation;

FIG. 6 is a greatly simplified representation of a portion of theapparatus illustrated in FIGS. l-S;

FlGS. 7 and 8 are graphs which are useful in explaining the operation ofapparatus embodying the present invention;

FIG. 9 is a view similar to the representation in FIG. l, but itillustrates another embodiment of the invention;

FiG. l() is a view of the apparatus of FIG. 9 taken in the direction ofarrow 1l);

FIG. ll is va cross-sectional view taken along line .11-1-1 of FIG. l0;

FIG. l2 is a view similar to FlG. 4, but illustrating still anotherembodiment of the invention;

FIG. 13 is -a cross-sectional view taken along line 13-13 of FIG. l2;and

FIGS. 14-17 represent various modilications which may -be made toapparatus embodying the present invention.

In FG. 1 of the drawings, apparatus embodying the present invention isshown to be comprised of a housing or mandrel 10 suspended by a cable 11in a borehole 12 which is drilled into earth formations 13. The borehole12 may or may not be illed with the usual drilling mud and by means of awinch (not shown) upon which the cable 11 is spooled, the housing 10 islowered and raised through the borehole 12 in a customary manner. Thehousing 1G may be of conventional pressure-resistant constructionarranged to contain any of various types of apparatus for exploring theborehole .or the earth formations. Apparatus for these purposes isconventional and forms no part of the present invention; consequently, adetailed description is deemed unnecessary. For the purposes of thepresent discussion, lit is suiicient to assume that housing 19 is to bemaintained in -a given p0- sition, for example, with its longitudinalaxis 14 in alignment with the longitudinal axis of borehole 12 as theinstrument is passed through the borehole, and apparatus embodying thepresent invention is ideally suited to this task.

Slidably supported on mandrel 10 are upper and lower collars 15 and 16.The interior dimensions of the collars 15 and 16 are arranged in a knownmanner so that mandrel 10 acts as a guide constraining movement of thecollars relative to one 4another along longitudinal axis 14. The portionof the apparatus thus far described constitutes a support assembly ofwhich mandrel 10 may be termed a support member whose outer surfaceforms a guide section on which mountings 15 and 16 are carried. Themountings 15 and 16 are, of course, operaapparsa tively associated withthe guide section so that one is movable relative to the other.

Extending between the collars or mountings and 16 are three armassemblies 17, 18, and 19. As shown in FIG. 2these assemblies are spacedequally about hous- Y ing 10 and portions thereof extend away from theaxis 14 toward the sidewall of the borehole 12. They are of identicalconstruction and thus only a single arm assembly, namely Ithe onenumbered 17, will be vdescribed in detail.

VAs best seen in FIG. 3, arm assembly 17 includes an upper arm 20 havingits upper end 21 tted into an appropriate recess 22 in collar 15. End 21ssuitaoly shaped and is provided with an opening (not shown) that` isaligned with complementary openings in the collar 15 all of winchreceive a pivot pin 23. Thus, arm 20 is connected at its end portion 21to collar 1S by a pivotal connection which constrains the arm forsubstantially onlyV pivotal movement, relative to the collar, about anaxis 24.

At its lower end arm 20 is provided with a yoke-shaped portion 25 whichreceives an appropriately shaped upper end pontion 26 of a lower -arm27. Complementary openings through the yoke 25 and end portion 26 of arm27 receive a pivot pin 28. The connection lthus formed between the armsconstrains them for substantially only pivotal movement relative to oneanother about an axis 29.

The lower end 30 of arm 27 is received within a recess y31 in lowercollar 16 and complementary openings through the collar `and end portion3l) receive a pivot pinl 32. This connection `constrains the arm 27 forpivotal movement relative to lower collar 16 about a given axis 33.

Assuming for the moment'that the arm assemblies 17, 18 and 19 are biasedoutwardly relative to support member 10 and engage the sidewall ofborehole 12, it will be K apparent that as the apparatus is lowered intoIthe borehole, the collars 15 and 16 Will slide upwardly along thesupport 10 and to limit such movement, a stop or abutment 34 is securedto the housing for engagement by the upper surface of lower collar 16.`Likewise, when the vapparatus is moved upwardly another stop or abutment35 engages the lower surface of upper :collar 15. Accordingly, movementthrough the borehole in both directions isV facilitated.

IIt has been discovered that the arm assemblies may be biasedV outwardlyin a relatively simple and efticient manner by constructing fthe arms ofa resilient material such as steel permitting the arms to bend Whilemaintaining essentially -ixed lengths and orienting the axes 24, 29 and33 so that at least two are not parallel to one another. In particular,as seen in F'IG 4A, the orthogonal projections of axes 24 and 29 inV aplane perpendicular to-arm 20 (when arm' 20 is unstressed) dene a givenang-le A while the corresponding orthogonal projections of axes 29 and33 in a' plane perpendicular to arm 27 (when arm 27 is unstressed) dennea similar angle A' (FIG. 4B); Thus, axes 24 and 29 are nonparallel andaxes 29 and 33 are nonparallel. As seen in FIG. 3, the axis 24' makes anangle B with a plane 36 perpendicular to longitudinal axis 14 and axis33 defines a similar angle B with another plane 37 perpendicular tolongi- Itudinal axis 14. The angles B and B will be discussed more fullyhereinafter.V

Ingoperation, as .the apparatus moves through borehole 12 and theborehole diameter decreases, arm assemblies 17-19 are driven inwardly.Of course, collars 15 and 16 are displaced away from one another toaccornc 4 condition with the arms substantially completely collapsedinwardly, a condition as shown in FIG. 5 lobtains with the bow of muchsmaller radius R. The resiliency of the arms 20 and 27, or" course, tendto restore the assembly 17 to an unstressed conditionlrepresented inbroken outline in FIGS. l and 2) and thus the arms 2d and 27 are biasedoutwardly relative to support 1th. lIt is thus Vapparent that as theapparatus embodying the present invention is passed through borehole,the arm assemblies 17, 1S and 19 compress inwardly as the boreholediameter decreases but because of the action just described, a resilientrestoring force tends to expand the arm assemblies and maintain them incontact with the sidewall despite changes in borehole diameter.

Obviously, it is important for the several pivotal con- Y ately chosen.Further, the arms can be olset relative to their end portions 21 and 31,as shown, so that as the arms 2o and 27 bend, portions 25 and 26 movefrom one side to the other of a vertical plane detined by the axis ofsupport 1t) and portions 21 and 31.

To' analyze the operationof apparatus embodying the present invention,reference is made to FIG. 6 which is a greatly simpliiied representationof upper arm 29, illustrating it as being movable between a horizontalplane and vertical axis 14. Since the arms 20 and 27 are identical, ananalysis of the static conditions on a single arm will be Vsufficientfor the purposes of the following discussion. eIn

FIG. 6, broken line U represents the unstressed position of arm 20,displaced by an angle C from the horizontal plane. As Will be evidentfrom the discussion to follow, position U may be selected to provide adesired range of operation for arm 20.

It may be shown that the tangential restoring force Ft maybe expressedas follows:

EI sin2 A cos 6 sin 9 L21/ l-sin2 A sin2 0 where Eis the modulus ofelasticity of the arm material, I is the moment of inertia of the arm, Lis the length of the arm, and 0 is the angular displacement of the armfrom Fa: 24.8 sin 0 cos 6 (2) 1/1-.os01 sini a From FIG. 6 it may beseen that the radial or lateral restoring force P is: Y

P=Es sin 0 (3) and substituting the expression for Ft from Equation 2into Equation 3 it will be seen that 24.8 sin2 9 cos t2 t/l-.oaol S1112e Y In FIG. 7, the relationship expressed in Equation 4 is representedgraphically by curve 38 which demonstrates that the lateral force inpounds increases as the angular displacement increases. It reaches amaximum value in the neighborhood of 50 to 60 degrees and then decreasestoward zero as the displacement approaches degrees.

It is also evident that the lateral force becomes negative beyond 90degrees.

If, for example, it is desired to obtain a relatively constant forceover a desired range of angular displacement, a selected portion of thecharacteristic represented by curve 38 may be used. For example, let itbe assumed that a range of borehole diameters from 6 inches to 16 inchesis to be accommodated. In FIG. 8, curve 39 represents the lateral extentof a 10-inch arm as a function of angular displacement from verticalaxis 14. For a lateral change of ive inches (which is the maximum changerequired for the selected range of diameters), a 30 degree change in armdisplacement is required. Referring again to FIG. 7, it will be observedthat the portion of curve 39 of most desirable shape occurs over a 30degree change in 6 from 40 degrees to 70 degrees.

If arm 20 is in its unstressed condition when aligned with thehorizontal plane (FIG. 6), angle B (FIG. 3) is equal to angle A of FIG.4A. In order to operate the arm in the desired range from 4() degrees to70 degrees, it is necessary to displace the unstressed condition by anangle C, represented in FIG. 7 as 20 degrees. Angle B of FIG. 3 (as wellas angle B') may be calculated from the following relationship:

Tan B= COS C voor? A-l-sin2 C If angle A is assumed to be 1() degrees toprovide a reasonable limit to the stresses developed in the arm, fromEquation 5, angle B may be found to have a value of 8 degrees, 40minutes. With these values, the lateral force developed by arm 26 as afunction of angular displacement 0 exhibits a characteristic representedby broken line 40 in FIG. 7 and the useful range of displacement occursfrom 60 to 90 degrees. It will be noted that the lateral force developedthrough this range varies between 71/2 and 10 pounds. Obviously, arelatively constant wallengaging force is featured over the desiredrange of borehole diameters.

It is therefore evident that apparatus embodying the present inventionmay be employed to center an instrument within a borehole whileoperating efliciently and effectively over a relatively large range ofborehole diameters. In addition, it is evident from the example given,in which arms l0 inches in length are employed, that the apparatusembodying the invention is relatively small in its longitudinaldimensions. Further, apparatus embodying the invention can be arrangedto provide a selected force versus lateral deliection characteristics.It may be arranged to be relatively constant or it may be designed toprovide a variety of different characteristics. For example, byappropriate selection of the angles A and B it is possible to obtain anaction which produces an outward biasing force over one range while uponreaching another range an inward biasing force is eiected (note thenegative region of curve 38 in FIG. 7). It is further evident thatapparatus embodying the present invention is relatively simple toconstruct while operating consistently to provide accurate centering ofa borehole instrument despite the changes in the borehole diameter.

It is also evident that angles A and A while of equal value are ofopposite sign (FIGS. 4A and 4B). Accordingly, although the arms 21) and27 deilect sideways as the apparatus operates, relative torque betweenthe collars and 16 is essentially Zero. -Further, within the limits ofthe strength of the materials, by increasing angle A the lateral forcemay be increased to any desired value.

In the embodiment of the invention illustrated in FIG. 9, a support formandrel 41 carries upper and lower slidable collars 42 and 43 and an armassembly 44 extends between the collars. The assembly 44 is comprised ofan upper arm 45 pivotally connected at its upper end 46 to collar 42 sothat movement relative to the collar is constrained about a pivotal axis47 (FIG. l0) whose orthogonal projection in a plane containinglongitudinal axis 48 of mandrel 41 is perpendicular to the longitudinalaxis 48. At its lower end 49, arm 45 is pivotally connected to upper endportions 5t) and 5l of lower arms 52 and 53. These pivotal connectionshave a common pivotal axis 54 whose orthogonal projection irl a planecontaining axis 4S is perpendicular to axis 4S. The lower ends 55 and 56of arms 52 and 53 are pivotally connected to lower collar 43 formovement about axes 57 and 5S, respectively. Assuming that the arms 52and 53 are in their unstressed conditions, the orthogonal projections ofthe axes 57 and 58 land the orthogonal projection of pivotal connection54 in a plane perpendicular to the arms 52 and 53 denne equal butopposite angles E and F as represented in FIG. ll. [Further, as seen inFIG. l0, the axes 57 and 58 deline with respect to a horizontal plane 59angles G and H of equal and opposite values. It is evident that byconstructing arms 52 and 53 of a resilient material such as steel and byutilizing pivotal connections of appropriate strength the action of armassembly 44 is essentially like the action of arm assembly 17 of theembodiment of FIGS. l-5. Since angles E and F are of opposite sign, thearms 52 and 53 bow away from one another as the arm assembly 44 isdeliected inwardly and the resilient restoring force in the arms tendsto bias the arm assembly outwardly, thus causing its outer extremity to@follow the wall of a borehole. IFurther, by suitably selecting angles Eand F a desired amount of force, within the elastic limit, can beobtained. Moreover, an appropriate selection of angles G and H willprovide an unstressed condition for the arm assembly at a selectedposition. Accordingly, a substantially constant lateral force may beobtained over a desired range of borehole diameters in essentially thesame manner explained in connection with FIGS. 6-8.

Referring now to the embodiment of the invention illustrated in FIG. l2,mandrel 6G slidably carries a pair of collars 61 and 62 to which an armassembly 63 is connected at its upper and lower ends. The arm assembly63 is comprised of an upper arm 64 and the lower arm 65 whose upper andlower ends, respectievly, are pivotally connected to the collars 61 and62 for movement about axes `66 and 67. The orthogonal projections of theaxes 66 and 67 in a plane containing longitudinal axis 68 areperpendicular to the axis 68. Adjacent end portions of the arms 64 and65 are connected together for pivotal movement about an axis 69. In theunstressed condition of the arms 64 and 65, the orthogonal projectionyof the axis 69 in a plane perpendicular to either of the arms 64 and 65is inclined relative to the orthogonal projection of the correspondingone of the axes 65 or 67 in the corresponding plane. With thisnonparallel axis arrangement, it is obvious that the same type of actiondescribed in connection with the embodiment of lEIGS. l-5 is achieved.However, it is evident that a relative torque will be developed betweencollars 6l and 62 so that in order to retain a desired lateral biasingforce, it may be desirable to provide keyed connections between thecollars 61; and 62 and the mandrel 6i), for example, in a manner to bedescribed later in connection with FIG. 14. Thus, the collars areconstrained against rotational movement relative to the mandrel 6G whilesliding longitudinal movement is permitted.

Relative torque between the collars 6l and 62 may be avoided by the useof another arm assembly 7l), illustrated in FIG. 13, positioned on aside of the mandrel 69 opposite to arm assembly 63. In arm assembly 70,a pivotal connection between the upper and lower arms has a pivotal axis71 which has essentially the same inclination as axis 69 but is ofopposite direction. Accordingly, relative torque developed by the armassemblies 63 and 7G is fully counterbalanced.

Although slidable collars on a mandrel have been illustrated inconnection with the embodiments of the invention ydescribedhereinbefore, obviously other mounting Vcilitate its passage through aborehole.

'terial.

apparsa 7 arrangements are entirely suitable in the application of thepresent invention. For example, as shown in FIG. 14, an upper mounting72 maybe provided with a downwardly-extending, integral shaft 73 that isslidably received .within a closely-tting opening or bore 74 in a lowermounting 7S. A key 76 on shaft 73 cooperates with Va keyway 77 cutV intothe wall of bore 74 to prevent relative rotation -between'the mountings72, 7 5 while permitting relative longitudinal movement. One or moreYarm 'assemblies such as the one designated 17 (corresponding to thesimilarly-identied arm in the-embodiment of FIGS. 1-5) may be connectedbetween the mountings 72 and 75 to provide the unique action describedin connection with the present invention.

If desired, appropriate means may be included for i displacing themountings 72 and 75 away from oneranother thereby to retract the armassembly 17 and fa- Any of various formsY of mechanical or hydraulicmechanisms of welllknown construction may be employed. For example,

the lower end of shaft 73 may be provided with an appropriate rack 78and a pinion 79 supported for meshing engagement with the rack 78 isarranged to be driven lby an electric motor 8G. Appropriate electricalconnections -(not shown) extend Yto the surface of the earth 'where asource of electrical energy (not shown) may 'he connected to energizethe motor. Thus, at the option of Yan operator, the motor 89 may beenergized to drive the rack 78 upwardly and an appropriate lockingmechanism (not shown) may Ibe provided so that the motor Vmay be4cle-energized While the mountings 72 and 7S re- Vmain in a selectedlongitudinally spaced condition.

' borehole and thus -avoid or minimize fouling of the pivotal connectionbetween the upper and lower arms by Wall rn a- Alternatively, thepivotal connection may be encased in a suitable huid-tight housing suchas illustrated in FIG.V15. Thus, the pivotal connection between theupper and lower arms of arm assembly 17 is encased ina molded rubberhousing S1 which has a portion 82 of reduced cross-sectional area in aplane transverse tothe pivotal axis 29. In this way, pivotal movementbetween the arms 20 and 27 is unimpeded. Portions 83 and S4 of thehousing 81 which are above and below the reduced section 82 extendoutwardly toward the wall of the borehole and thus provide appropriatewall-contact portions which are displaced longitudinally from the axis29. It is thus evident that the pivotal connection between the arms 29and 27 is protected, appropriate wall-engaging portions are providedand, at the same time, pivotal movement between the arms is notimpaired.

Apparatus embodying the present invention may also Vbe used formaintaining a wall-engaging instrument in a desired position withrespect to the sidewall of the borehole as'it is passed through theborehole. For example, as shown in FIG. 16, an arm assembly 90 which maybe similar to arm assembly 44 in the embodiment of FIGS.

v9--11 is pivotallypconnected at its upper and lower ends to collars 91and 92 which are slidably supported Yon a mandrel 93. Another arm 94positioned above the upper arm of the arm assembly 9&3 is pivotallyconnected to the collar 91 at one end and is pivotally connected at itsouter end to the rear of a wall-engagingdevice 95.' An extension 96 ofthe upper arm of arm assembly 9) is also pivotally connected to the rearof the wall-engaging device 95. The upper arm of Vassembly 9d and arm 94have their pivotal connections arranged to form a parallelarm linkage ofa type such as described in Patent No. 2,876,413. Thus, thewall-engaging device 95 is maintained in a predetermined relationshiprelative `to mandrel'93 as it is urged into biasedengagement with thesidewall of a borehole 97 by the action of arm assembly '90. i

lfdesired, a similar arrangement may be provided on the side of mandrel93 opposite to arm assembly 99 -so that two wall-engaging members may bemaintained Vin contact with opposite sidewall portions of the borehole97. 0n the other hand, the mandrel 93'may itself be maintained againstthe sidewall of the boreholeand appropriate wall-contact members orbumpers 93 and 99' may be provided for this purpose. Wall-engagingdevice 95 may carry any of a variety of sensing elements in the form ofeither electrodes or other means for investigating the characteristic ofthe earth formation penetrated'byV the borehole 97.

It is evident from the illustration of FIG. 16, that apparatus embodyingthe present invention may be utilized to maintain a device such as thepad V95 in engagement with the sidewall of the borehole or formaintaining an instrument contained within mandrel 93 in an eccenteredposition relative to the axis of the borehole. ,n

Obviously, since the lateral'position of an arm assembly featuring thepresen-t invention is dependent upon the diameter oiga borehole throughYwhich it is passed, that parameter may be measured. Thus, either theposition of an arm relative to the mandrel or the relativespacingbetween the mountings or collars may be sensed by any of variousconventional devices to provide indications of borehole diameter. Forexample, an arrangement such Yas disclosed and claimed in Patent No.2,712,697 is illustrated in FiG. 17. A lower collar 16 is slidable on amodified housing 1li constructed of a nonmagnetic material. Collar 16 isconnected to another collarltltl constructed of a ferromagnetic materialand provided with helicoidal slot 191. Rotatably supported within theVhousmg is a horse shoe shaped magnet 102 mechanically connected to avariable resistor 193i. Leads 164 extend from variable resistor 193through an electric cable 105 to la resistance-measuring circuit 106 atthe surface` of the earth. Circuit 196 is connected to an appropriaterecorder 107 in which the recording medium is displaced in aconventional manner in proportion to movement of the housing 1li througha borehole '108.

As the instrument passes through the borehole, varia- 'tions in theborehole diameter produce movement of the collar 16 and thus magneticelement 166 is positioned longitudinally relative to housing 10 as afunction of borehole diameter. Because of the presence of helicoidalVslot 191, magnet 102 likewise is positioned in rotationk as a functionof borehole diameter yand resistance element 193 exhibits acorresponding resistance value. Resistance-measuring circuit 196develops a voltage dependent "upon the resistance value of element 193'and thus recorder 197 provides a record of borehole diameter as afunction of depth. I

As described earlier in connection with the embodiment of FIGS. 1-5, anarm assembly constructed in accordance with the present invention isconsistently maintained in engagement with the sidewall of the borehole.Accordingly, the arm assemblies in the embodiment of FIG. 17 eiiicientlyand eiiectively respond to changes in borehole diameter and accurateindications are provided.

While particular embodiments of the present invention have been shownand described, it is apparent that changes and modifications may be madewithout departing from this invention in its broader aspects, Iandtherefore the aim in the appended claims is Yto cover all such changesand modications as fall within `the true spirit and scope of thisinvention.

What is claimed is:

1. Apparatus for maintaining borehole equipment at a l relative to theborehole; a pair of mountings carried by said support member, one `ofsaid mountings being operatively associated |With said guide section formovement relative to the other of said mountings; and a pair of armsincluding adjacent portions pivotally connected to one another andopposed portions pivotally connected to respective ones of saidmountings, the axes of at least two of the pivotal connections beingnonparallel to one another, and one of said arms being formed of a barof resilient material.

2. Apparatus for maintaining borehole equipment at a given positionrelative to the central axis of a borehole comprising: ya support memberadapted for use in a borehole and having -a guide section extendinglongitudinally relative to the borehole; a pair of collars carried bysaid support member, said collars being slidably associated with saidguide section for limited movement relative to each other; land threepairs of arms, each of said pairs including adjacent portions pivotallyconnected to one Vanother and opposed portions pivotally connected toand equally spaced about respective ones of said collars, the axes of atleast two of lthe pivotal connections being nonparallel to one another,and one arm of each of said pairs being formed of a bar of resilientmaterial permitting said one a1m to ex upon the application thereto of abending moment so as to bias said adjacent portions of said arms awayfrom said support member and toward the sidewall of the borehole.

3. Apparatus for maintaining borehole equipment at a given positionrelative to the central axis of a borehole comprising: a support memberadapted for use in a borehole and having la guide section extendinglongitudinally relative to ythe borehole; a pair yof mountings carriedby said support member, one of said mountings being operativelyassociated with said guide section for movement relative to the other ofsaid mountings; and a pair of arms including adjacent portions pivotallyconnected to one another and opposed portions pivotally connected torespective ones of said mountings, the axes of at least two of thepivotal connections being nonparallel to one another, one of said yarmsbeing formed of a bar of resilient material, and one of said adjacentportions of said arms having a Wall-engaging member movable therewith.

4. Apparatus for maintaining borehole equipment at a given positionrelative to the central axis of -a borehole comprising: ya supportmember adapted for use in a borehole and having a guide sectionextending longitudinally relative to the borehole; a pair of mountingscarried by said support member, one of said mountings being operativelyassociated with said guide section for movement relative to the other ofsaid mountings; and at least one pair of arms of substantially ixedlength including adjacent portions pivotally connected to one anotherand opposed portions pivotally connected to respective ones of saidmountings, the axes of at least two of the pivotal connections beingnonparallel to one another, and one of said arms being constructed of aresilient material and thereby adapted to flex upon the Iapplication ofa bending moment.

5. Apparatus for maintaining borehole equipment at a given positionrelative to the central axis `of a borehole comprising: a support memberadapted for use in a borehole iand having a guide section extendingalong a longitudinal axis oriented in substantially the same directionas lthe vertical axis of the borehole; a pair of mountings carried bysaid support member, one of said mountings being operatively associatedwith said guide section for movement relative to the other of saidmountings; and a pair of arms including Iadjacent portions pivotallyconnected to one another and opposed portions pivotally connected torespective ones of said mountings, one of said `arms being formed of abar of resilient material and the :axes of at least two of the pivotalconnections being nonparallel to one another as viewed in orthogonalprojections upon a plane containing said longitudinal axis.

6. Apparatus for maintaining borehole equipment at a given positionrelative to the central axis of a borehole comprising: a support memberadapted for use in a borehole and having a guide section extendinglongitudinally relative to the borehole; a pair of mountings carried bysaid support member, one of said mountings being opertatively associatedWith said guide section for movement relative to the :other of saidmountings; at least one pair of arms including adjacent portionspivotally connected to one another and opposed portions pivotallyconnected to respective ones `of said mountings, the axes of at leasttwo of the pivotal connections being nonparallel to one another, and oneof said arms being formed of a bar of resilient material; and means forobtaining indications in response to relative movement between saidmountings.

7. Apparatus for maintaining borehole equipment at a given positionrelative to the central axis of fa borehole comprising: a support memberadapted for use in a borehole and having a guide section extendinglongitudinally relative to the borehole; a pair of mountings carried bysaid support member, one of said mountings being oper- Iativelyassociated with said guide section for movement relative to the other ofsaid mountings; and a pair of Iaims including adjacent portionspivotally connected to one another and opposed portions pivotallyconnected to respective ones of said mountings, the axes of the twolast-mentioned pivotal connections being nonparallel to one another andto the iirst-mentioned pivotal connection, and one of said arms beingformed of a bar of resilient material.

8. Apparatus for maintaining borehole equipment at a given positionrelative to the central axis of a borehole comprising: a support memberadapted for use in a borehole and having a guide section extendinglongitudinally relative to the borehole; a pair of mountings carried bysaid support member, one of said mountings being operatively associatedwith said guide section for movement relative to the other of saidmountings; and a pair of arms including adjacent portions pivotallyconnected to one another and opposed portions pivotally connected torespective ones of said mountings, the axis of the first-mentionedpivotal connection and the axis of one of the lastmentioned pivotalconnections being nonparallel to one another as viewed in orthogonalprojections on a plane 4substantially perpendicular to a correspondingarm, and one of said arms being formed of a bar of resilient material.

9. Apparatus for maintaining borehole equipment at a given positionrelative to the central axis of a borehole comprising: a support memberadapted for use in a borehole and having a guide section extending alonga longitudinal axis oriented in substantially the same direction as thevert-ical axis of the borehole; a pair of mountings carried by saidsupport member, one of said mountings being operatively associated withsaid guide section for movement relative to the other of said mountings;and a pair of arms including adjacent portions pivotally connected toone another and opposed portions pivotally connected to respective onesof said mountings, one of said arms being formed of a bar of resilientmaterial, the axis of the irst-mentioned pivotal connection and the axisof one of the last-mentioned pivotal connections dem'ng a given anglewhen said one arm is in an unstressed condition, and the axis of one ofsaid firstmentioned and said one last-mentioned pivotal connectionsdening another angle with a plane perpendicular to said longitudinalaxis of a value different from the value of said given angle.

l0. Apparatus for maintaining borehole equipment at a given positionrelative to the central axis of a borehole comprising: a support memberadapted for use in a borehole and having a guide section extendinglongitudinally relative to the borehole; a pair of mountand twocoextensive arms separately and pivotally connected to the other of.said vmountings, adjacent portions `of said coextensive arms beingjointly and pivotally connected to Yan adjacent portion of saidfirst-mentioned arm, the .axesrof the three last-mentioned pivotalconnections being nonparallel to one another, and each of saidcoextensive arms be-ing formed of a bar of resilient material.

l1. Apparatus for maintaining borehole equipment at a given positionrelative to the central asis of a bore- 'hole comprising: a supportVmember adapted for use in -arborehole and having a guidesectionextending longitudinally relative to the borehole; a pair ofmountings Vcarried by said support member, said mountings beingoperatively associated with said guide section for limited movementrelative to each other; a pair of arms including lirst end portionsdisposed adjacent to respec- 'tive ones of said mountings, said armsextending Vaway from said support member toward the sidewall of theborehole and including other second end portions adjacent to oneanother; means for connecting each of said irst; endV portions of saidarms to a respective one of said mountings and for constraining saidfirst end portions for substantially only pivotal movement relative tosaid mountings about respective, given axes; means 'for connecting saidsecond end portions of said arms to one another and for constrainingsaid second end portionsy for substantially only Vpivotal movementrelative to one another about another given axis, at least two of theaforesaid axes being nonparallel to one another, and one of said armsbeing formed of a bar of resilient material.

l2. Borehole apparatus comprising: a support adapted to be passedthrough a borehole; a pair of mountings carried by said support formovement relative to one another along a fixed path; a iirst pivot arm;a second pivot Yarm being constructed of a resilient material permittingsaid second pivot arm to tien upon the application of a'bending moment;a iirst pivotal connection between said irst pivot arm and one of saidmountings; a second pivotal connection between said second pivot arm andanother of said mountings; and a third pivotal connection between saidfirst and said second pivot arms,

-at least two of said pivotalY connections having pivot axes nonparallelrelative torone another.

13. Borehole apparatus comprising: a mandrel adapted to be passedthrough a borehole; a pair of collars mounted on said mandrel, at leastone of said collars being slidable thereon for movement relative to theother col- Vlar along a iixed path; a irst pivot arm; a second pivot armconstructed of a resilient material permitting said second pivot arm toilex upon the application of a bending moment; a rst pivotal connectionbetween said irst pivot arm and one of said collars; a second pivotalconnection between said second pivot arm and another of said collars;and a third pivotal connection between said first and said second pivotarms, at least two ot said pivotal connections having pivot aXesnonparallel relative to one another.

14. Borehole apparatus comprising: ya mandrel adapted to be passedthrough a borehole; a pair of collars mounted on said mandrel, Kat leastone of said collars being slidable thereon for movement relative to theother collar along a lxed path; iirst and second pivot arms eachconstructed of a resilient material permitting flexure upon theapplication of ka bending moment, said pivot anms .'being ofsubstantially iixed length; a iirst pivotal connection mechanicallycoupling said iiirst pivot arm and one of said collars; a second pivotalconnection mechanically coupling said second pivot arm and another ofsaid collars; and a third pivotal connection mechanically coupling saidiirst and said second pivot arms, at least twovof said pivotalconnections having pivot axes nonparallel relative to one another.

l5. Borehole lapparatus comprising: a mandrel adapted to be passedthrough a borehole; a pair ot collars mounted on said mandrel, at leastone of said 'collars be- Vving slidable thereon for movement relative tothe other collar along a lfixed path having a longitudinal axis relativeto the borehole; rst and second pivot arms each constructed of aresilient material permitting iiexurey upon the application of a bendingmoment, said pivot Iarms being of substantially iixed length; -a iirstpivotal connection mechanically coupling said first pivot arm and one ofsaid collars; a second pivotal connection mechanically coupling saidsecond pivot arm and another of said collars; and a third pivotalconnection mechanically coupling said iirst and said second Vpivot arms,said irst and said third pivotal connections having pivot laxes Whoseorthogonal projections in a plane perpendicular to 4a corresponding oneof sai-d arms define a given angle when said one arm is in anlunstressed condition.

16. Borehole apparatus comprising: a mandrel adapted to be passedthrough a borehole; a pair of collars mounted on said mandrel, at leastone of said collars being slidable thereon `for movement relative to theother collar along a iixed path having an axis extending longitudinallyrelative to the borehole; la first pivot anni; a Asecond pivot armconstructed of a resilient material permitting said second Vpivot arm toflex upon the Iapplication of a bending moment; a iirst pivotalconnection mechanically coupling said rst pivot arm and one of said col-`lars; a second pivotal connection mechanically coupling said secondpivot arm and another of said collars; and a third pivotal connectionmechanically coupling said tirst and said second pivot arms, said secondand said third pivotal connections hav-ing pivot axes Whose orthogonalprojections in a plane perpendicular to the corresponding one of saidarms define a lgiven angle when said one arm is in an unstressedcondition, and the pivot axis of one of said second and said thirdpivotal connections deiining another angle with a plane perpendicular tosaid longitudinal axis of a value ditferent from the value of said givenangle.

17. Borehole apparatus comprising: a support adapted to be passedthrough a borehole; a pair of mountings carried by said support formovement -relative to one another along a 'fixed path; a rst pivot arm;second and third coextensive pivot arms, each of said arms constructedof a resilient material permitting iiexure upon the application of abending moment; a pivotal connecytionibetween said tirst pivot arm andone of said mountings; a pair of adjacent pivotal connections betweensaid second and third pivot arms and another of said mountings; andanother pair or" adjacent pivotal connections between said rst pivot armand said second and third pivot arms, said ynist-mentioned pair ofpivotal connections having pivot axes nonparallel relative to oneanother.

128. In combination: a support; a pair of mountings carried by saidsupport for movement relative to one another along a .fixed path; aiirst pivot arm; a second pivot arm constructed of a resilient materialpermitting said second pivot arm to flex upon the application of abending moment; a first pivotal connection between said iirst pivot armand one of said mountings; a second pivotal connection between saidsecond pivot arm and anoth- `er ofsaid mountings; and a third pivotalconnect-ion between said first and said second pivot arms, at least twoof said pivot-al connections having pivot axes nonparallel relative toone another. Y

19. In combination: a mandrel; a pair of mountings carried by -saidmandrel, one of said mountings being mounted for movement relative tothe other along a iixed path; a :first pivot arm; a second pivot armconstructed of a resilient material permitting said second pivot 4arm toflex upon the application of a bending moment; a first pivotal`connection between said first pivot am and one of said mountings; -asecond pivotal connection between said second pivot arm and another ofsaid 5 mountings; and `a third pivotal connection between said iirst andsaid second pivot arms, said second and said ythird pivotal connectionshaving pivot axes inclined relative to one another as viewed inorthogonal projections in a plane perpendicular -to said second arm whensaid 10 second arm is in an unstressed condition.

References Cited in the le of this patent UNITED STATES PATENTS BaileyFeb. 21, Crawford July 8, McCray Feb. 23, Segesman Nov. 30, Roussin Nov.12, Hall May 12, Smith et a-l. Aug. 11,

1. APPARATUS FOR MAINTAINING BOREHOLE EQUIPMENT AT A GIVEN POSITION RELATIVE TO THE CENTRAL AXIS OF A BOREHOLE COMPRISING: A SUPPORT MEMBER ADAPTED FOR USE IN A BOREHOLE AND HAVING A GUIDE SECTION EXTENDING LONGITUDINALLY RELATIVE TO THE BOREHOLE; A PAIR OF MOUNTINGS CARRIED BY SAID SUPPORT MEMBER, ONE OF SAID MOUNTINGS BEING OPERATIVELY ASSOCIATED WITH SAID GUIDE SECTION FOR MOVEMENT RELATIVE TO THE OTHER OF SAID MOUNTINGS; AND A PAIR OF 